1. Field
The present invention relates to two-stroke internal combustion engines and more particularly to such engines which incorporate a separate compressor.
2. Prior Art
In the vast majority of prior art two stroke engines, a mixture of air, fuel and oil is injected into the crankcase where the mixture is compressed before it is fed to the cylinder head. FIGS. 1 through 3 are diagrams of a conventional two-stroke engine, showing various positions of the cylinder during the two-stroke cycle. The upper portion of the cylinder is referred to the cylinder head area while the lower portion is referred to as the crank case area. These Figures are identical except for the position of the piston within the cylinder. From these Figures, the engine can be seen to comprise a cylinder 1, a spark plug 2, a piston 3, a connecting rod 4, a flywheel 5, a pin through the piston 6, a crankshaft 7, a bypass 8, an exhaust port 9 and an air-fuel-oil input port 15.
In the operation of this prior art engine, the piston moves up and down within the cylinder. The piston is attached to one end of the connecting rod by pin 6 while the opposite end of the connecting rod is rotatably attached to the crankshaft. The reciprocating motion of the piston is converted to rotational motion by way of the crankshaft. The crankshaft motion drives the flywheel 5. The piston can be seen to be positioned at the beginning of the up-stroke in FIG. 1. In FIG. 2, the piston has progressed farther up the cylinder, but has not reached the top of its stroke. In FIG. 3, the piston has passed the top of its stroke and is on the down strokes. As the piston starts the up-stroke, it draws into the crankcase an air-fuel-oil mixture through the input port 15. Above the piston in the cylinder area is an air-fuel-oil mixture which was forced into this area from the crankcase through the bypass during the previous cycle. The bypass is a passageway which connects the crankcase with the cylinder head. The piston can block the upper end of the bypass depending on its position within the cylinder. The position of the piston in FIG. 1 leaves unblocked both ends of the bypass 8, allowing the mixture to flow from the crankcase into the cylinder head area.
As the piston moves farther up in the cylinder, as shown in FIG. 2, the mixture in the cylinder head area is compressed. At the top of the stroke, the spark plug 2 ignites the mixture, forcing the piston down into a down or power stroke, as shown in FIG. 3. It can also be seen in FIG. 3 that on the down stroke, the piston blocks the upper end of the bypass 8 and at the same time, compresses the mixture in the crankcase area. As the piston proceeds lower, it comes to the position shown in FIG. 1 where the piston unblocks the upper end of the bypass, letting the mixture, which is now under pressure from the down stroke, flow through the bypass and enter the cylinder head area.
It can also be seen in FIG. 1 that the burnt mixture from the power stroke can escape through the exhaust port while the cylinder head area is being supplied with a fresh air-fuel-oil mixture from the crankcase. The fresh mixture from the bypass is under pressure and it aids in forcing the burnt mixture out through the exhaust port.
The advantage of a two stroke engine is it produces two power strokes within four strokes which, considered by itself, would theoretically produce double the power output of a four cycle engine having the same piston displacement; however, there are several disadvantages to the two stroke engine. One is fuel laden air is used to help purge the cylinder of fumes which invariably loses fuel through the exhaust pipe and lowers efficiency. A second disadvantage is that the lubricating oil has to be mixed with the fuel because a conventional splash lubricating system cannot be placed in the crankcase area of the cylinder. If oil, which is typically available in abundance in the crankcase area, is splashed about as is normal in a conventional lubrication system, this abundance of oil would unbalance the air-fuel-oil mixture necessary for the two stroke operation.
A number of inventions have been made to improve two stroke engines, and some have been directed at improving the lubrication system, but none have been directed at eliminating in one engine all of the shortcomings noted above. The following patents illustrated some of the prior art inventions in this area.
U.S. Pat. No. 4,206,727 illustrates a two stroke engine which has a main piston, an auxiliary piston and transfer valve arrangement with its associated drive mechanism.
U.S. Pat. No. 4,579,093 illustrates a two stroke spark ignition engine designed to eliminate the need for the typical reed valve and carburetor, and also eliminate the carbon build up inherent in the mixing of the lubricant with the fuel mixture.
U.S. Pat. No. 5,638,779 illustrates an internal combustion engine of either two stroke or four stroke construction which includes a block having at least one cylinder bore therein, having sidewalls carrying a liner of a structural fiber reinforced ceramic matric.
U.S. Pat. No. 6,478,642 illustrates an oil system for a two stroke outboard marine engine. The oil system includes a housing for the oil system which contains an inlet, an outlet and an oil return.
U.S. Pat. No. 6,513,464 illustrates a stratified two cycle engine comprising a cylinder having an upper end and a lower end, a head at the upper end and fuel and air intake ports at the lower end.
Although the prior art patents provide some improvements over the disadvantages of a two stroke engine, they do not eliminate them entirely. The specific shortcomings noted above are eliminated in the present invention which is described below.